Apparatus for and method of de-waxing,presintering and sintering powdered metal compacts

ABSTRACT

IN THIS APPARATUS A DE-WAXING OPERATION IS PERFORMED IN HYDROGEN, AND THE SAME VESSEL IS USED FOR VACUUM SINTERING WITHOUT MOVING OF THE PART TO BE HEAT TREATED, AND IN ONE CONTINUOUS OPERATION.

Jan. 2, 1973 SCHEYER 3,708,285

APPARATUS FOR AND METHOD OF DE-WAXING, PRESINTERING AND SINTERINGPOWDERED METAL COMPACTS Original Filed July 25, 1969 3 Sheets-Sheet 1 60FIG. I 69 DRAIN INVENTOR.

GERARD SCHEYER Jan. 2, 1973 G. SCHEYER 3,708,285

APPARATUS FOR AND METHOD OF DE-WAXING, PRESINTERING AND SINTERINGPOWDERED METAL COMPACTS Original Filed July 25, 1969 3 Sheets-Sheet z:IZ -l JI'; INVENTOR. GERARD SCHEYER 95 94 ATTGRNEX 3,708,285PRESINTERING 3 Sheets-Sheet 3 G. SCHEYER POWDERED METAL COMPACTS Jan. 2,1973 APPARATUS FOR AND METHOD OF DE-WAXING AND SINTERING Original FiledJuly 25, 1969 aten 3,7@8,Z85 Patented Jan. 2, 1973 3,708,285 APPARATUSFOR AND METHOD OF DE-WAXING, PRESINTERING AND SIN'I'ERING POWDERED METALCOMPACTS Gerard Scheyer, Morris Plains, N..I., assignor to AdamasCarbide Corporation, Kenilworth, NJ.

Original application July 25, 1969, Ser. No. 844,972. Divided and thisapplication Jan. 14, 1971, Ser. No. 106,383

Int. Cl. 1322f 9/00; C22c 29/00 US. Cl. 75-221 11 Claims ABSTRACT OF THEDISCLOSURE In this apparatus a de-waxing operation is performed inhydrogen, and the same vessel is used for vacuum sintering withoutmoving of the part to be heat treated, and in one continuous operation.

This application is a division of my copending application Ser. No.844,972 filed July 25, 1969 now US. Pat. No. 3,654,374.

BACKGROUND OF THE INVENTION (1) Field of the invention This inventionrelates to apparatus for and process of heat treating metal powders suchas tungsten carbide that have been compacted cold and which contain aparalfin lubricant or binder, so that the lubricants or binder, arevolatilized and removed and sintered bring the compacts to finalhardness.

(2) Description of the prior art Heretofore the time cycles involvedwere such that the compacts went through the preheat, heat and cool-downprocesses in one furnace, and at room temperature, were thereaftertransferred into a sintering furnace for the sintering cycle.

SUMMARY OF THE INVENTION An object of this invention is to provide ahighly improved apparatus of the character described in which thede-waxing in hydrogen and sintering in vacuum is combined in a singlevessel without transfer of the compact from the vessel.

Another object of this invention is to provide a highly improved processof the character described comprising placing compacts in a pot which isplaced inside of a chamber; feeding hydrogen to the pot and feedingargon to the chamber; applying heat to the chamber so that the Waxes inthe compacts are volatilized and carried off through a removablegraphite chimney communicating with the pot, the argon protecting thegraphite components from oxidizing and excluding the air, then flushingout the hydrogen from the pot with argon, removing the chimney, placinga sight glass over the chimney opening, stopping all the gas flow andpumping out all gas from the chamber and pot to produce a vacuum andbringing up the heat to sinter the compacts in vacuum.

Yet another object of this invention is to provide in apparatus of thecharacter described, a highly improved cooled port through which thegraphite chimney passes, to keep the graphite cool and stop it fromoxidizing, and under vacuum operation when the graphite chimney has beenremoved and a sight glass has been installed, to prevent clouding up ofthe sight glass by preventing condensible vapors to settle on the sightglass.

Still another object of this invention is to provide a relativelyinexpensive apparatus of the character described which shall beeconomical to operate and which shall yet be practical and efficient toa high degree.

Other objects of this invention will in part be obvious and in parthereinafter pointed out.

The invention accordingly consists in the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter described, and of which thescope of invention will be indicated in the following claims. Theinvention also consists in steps of a process hereinafter described.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical axialcross-sectional view of apparatus embodying the invention and showingthe position of the parts during the de-waxing operation;

FIG. 2 is a cross-sectional view taken on line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 1;

FIG. 4 is a vertical cross-sectional view of the upper portion of theapparatus shown in FIG. 1 with the graphite chimney removed, the sightglass mounted on the cooled port and the swinging graphite sight holedisc or plate moved to center sight hole with the hole in the lid of theinner part; and

FIG. 5 is a piping diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to thedrawing, designates apparatus embodying the invention. Said apparatuscomprises an outer container 11 having an outer cylindrical wall 12 anda circular bottom wall 13 formed with a central hole 14. Within saidcontainer 11 is a circular inner bottom wall 15 spaced above wall 13.Mounted on wall 15 is an inner cylindrical wall 16. Between walls 12, 16and 13, 15 is a water jacket 17 closed at its upepr end by a ring 18. Awater inlet pipe 19 leads to the upper end of the jacket 17.

Attached to the underside of bottom wall 13 is a pipe 20 extendingdownwardly and closed by a plug 21 having a central opening 22. Pipe 20is provided with an outlet drain pipe 23.

Extending upwardly through center hole 22 of plug 21 is a stainlesssteel pipe 24 which passes through a central opening 25 in wall 15 andthereabove.

The pipe 24 extends below plug 21 and attached to its lower end is aT-fitting 26 having branches to which pipes 27, 28 are attached. Pipe 24is welded to wall 15 as at 29.

On top of wall 15 is a stool piece or base 30 having a central opening31 through which pipe 24 passes upwardly. Said base 30 has an outerupwardly extending flange 32. On base 30 is a cylindrical tube 33. Theupper end of pipe 24 is located below the level of the upper end of tube33. A ceramic tube 34 fits onto pipe 24 and rests on the base 30. Theupper end of tube 34 is located just below the upper end of tube 24.Between pipe 34 and tube 33 are vertical, circular graphite felt layers35. The layers 35 extend to a height just above the upper end of ceramicpipe 34 and rest on base 30. Mounted on the upper ends of layers 33 arecircular discs 36 of graphite felt. Said discs form multi-layers and aredisposed below the upper end of tube 33, and are formed with a centralhole 37. The pipe 24 reaches said central hole 37.

Mounted on top of tube 33 is a pot 40 having an outer cylindrical wall41 and a bottom wall 42 grooved at the periphery of its underside, as at42, to receive the upper end of tube 33. On top of pot 40 is a coverdisc 43 formed with a central opening 44 at the center of an upwardlyextending boss 45 formed with an outer downwardly divergentfrusto-conical surface 46. The tube 33, pot 40 and lid 43 are ofgraphite.

Extending through walls 12, 16 and the water jacket 17 is a horizontalpipe 50, the functions of which will be explained hereinafter. Alsopassing through walls 12, 16 and the water jacket 17 are three,equiangularly spaced, horizontal radiating tubes 51, the purpose ofwhich will be hereinafter explained.

On top of walls 12, 16 is a top closure 52 for the container 11. Saidclosure 52 comprises a circular wall 53 mounted on ring 18 and formedwith a central opening 54, and with an offset opening 55. Fitted ontowall 53 is a water jacket forming member 56 comprising a top wall 57from which a cylindrical flange 58 extends downwardly contacting andattached to the periphery of wall 53, and attached at its lower end edgeto the ring 18. Wall 57 has an opening 57a aligned with opening 55.Between walls 53 and 57 is formed a water jacket 60. Extending fromflange 58 is a water drain pipe 61. Top wall 57 has a central hole 62aligned with opening 54. Extending through openings 54, 62 is a shortvertical pipe 63 extending from the underside of wall 53 to above wall57. Pipe 63 is sealed to walls 5.3, 57.

At the upper end of pipe 63 is a pipe 64 having an inner diameter sameas pipe 63, and an outer upwardly divergent frusto-conical surface 65.

At the upper end of pipe 64 is a flange 66 having a central hole 67which may be of an inner diameter somewhat less than the inner diameterof pipes 63, 64. Flange 66 has bolt holes 68.

Mounted on flange 66 is a cooled port 69 comprising a lower flange 70having bolt holes 71 registering with bolt holes 68 to receive attachingbolts. Welded to the flange 70 are inner and outer concentric tubes 73,74, respectively forming a water jacket 75 therebetween. Welded to theupper end of said tubes 73, 74 is an upper flange 76.

Extending from the lower end of tube 74 is a Water inlet pipe 78.Attached to the upper end of tube 74 is a nipple 79. Surrounding theouter tube 74 is a tube of rubber or other heat insulating material.Outlet nipple 79 is connected by pipe 81 to an inlet nipple 82 leadingto water jacket 60.

Mounted on boss 46 of lid or cover 43 is a graphite chimney 85. Thelower end of chimney 85 has an internal beveled surface 86 resting onconical surface 46. Said chimney 85 passes upwardly through pipes 63, 64and through the cooled port 69 and thereabove. A thermocouple 86a passesdown through graphite pipe 85 and opening 44 into the pot 40. Theopening 44 is of greater diameter than the thermo-couple 86a.

Disposed within the container 11 is an insulating chamber 90. Saidchamber 90 comprises a cylindrical wall 91 surrounding the pot 40 andcomprising an outer perforated stainless steel cage 92 with graphitefelt layers 93 at its inside attached to said cage by moly clips 94which pass through holes 95 in the cage 92. Any other suitable attachingmeans may be employed.

At the lower end of cage 92 and attached thereto, is a circularhorizontal perforated stainless steel disc 96 formed with an opening 97through which tube 33 passes and which is located above base 30. On disc96 are flat layers 99 of graphite felt.

At the upper end of cage 92 is a perforated stainless steel disc 100disposed above pipes 50, 51 and located below wall 53 and formed with acentral opening 101 through which graphite chimney 85 passes. Attachedto the underside of disc 100 are layers 102 of graphite felt. These maybe attached by moly clips or in any other suitable manner.

Extending through pipes 51 are electric heating elements 104. Saidheating elements pass through openings 104a in chamber 90. Openings 104aare larger than the heating elements. Hung from these heating elementsand located in the chamber, are heating units 105 such as made by C. I.Hayes Inc. of Cranston, R1. for electric heat treating vacuum furnaces.The units 105 comprise graphite cloth pieces 106 to the lower ends ofwhich, arcuate weighted members 107 are attached.

Extending through openings 55 and 57a of walls 53, 57 of member 52, is avertical tubular bearing 110. Extending through said bearing 110 is avertical axle 111 of a crank member 112. At the upper end of axle 111 isa radial handle 113. Fixed to the lower end of axle 111 is a plate 114of somewhat elliptical shape. In FIGS. 1 and 2, the plate 114 is offsetfrom opening 54. Plate 114 comprises a top layer 114a of metal such asInconel 600 and four layers 114b of graphite felt cemented to layer 114aand to each other by graphite cement. Plate 114 has a through hole 115smaller than but centralized with respect to pipe 63 in the position ofFIG. 4 (with the graphite chimney 85 and the thermo-couple 86a removed).

Piping for supplying gases to the furnace and for creating vacuum isillustrated in FIG. 5. As shown, pipe 24 is connected to pipes 27, 28.Pipe 27 is connected through a hydrogen solenoid valve (to control flowof hydrogen to the pot 40), to pipe 121 in which is interposed ahydrogen flow meter 122 (to measure flow of hydrogen to pot 40). Pipe122 passes to a hydrogen shut off valve 123 (to shut off flow ofhydrogen to pot 40), to pipe 124 which leads to a hydrogen supply.Instead of pure hydrogen, dissociated ammonia may be used. Thedissociated ammonia comprises about 75% hydrogen and about 25% nitrogen.

Pipe 27 is connected through an argon solenoid valve 125 (to controlflow of argon to pot 40), to pipe 126 connected to an argon flow meter127 (to measure flow of argon to pct 40), which in turn is connected topipe 128. Pipe 128 connects to an argon shut off valve 129 (to shut 01fflow of argon to pot 40) which is connected to pipe 130 connected topipe 131 leading to a supply of argon.

Pipe or port 50 is connected through pipe 132 to a helium cool downvalve 135 which in turn is connected by pipe 136 to helium supply 137.

Pipe 50 is connected by pipe 138 to pipe 139 connected to an argon bleedvalve 140, which in turn is connected through pipe 141 to the argonsupply pipe 131. Pipe 139 is also connected to pipe 142 which connectsto an argon solenoid valve 144. Valve 144 connects to pipe 145 whichconnects to argon valve 147. Valve 147 connects to pipe 148 whichconnects to an argon flow meter 149. Said meter 149 connects to pipe 150which connects to pipes 141, 131. An argon pressure switch 152 connectsthrough pipe 153 to said pipe 150.

Pipe 138 connects to a pipe 154 which connects to a high vacuum valve155. Valve 155 connects to pipe 156 which connects to a booster pump157. Said booster pump connects through pipe 158 to a pipe 159. Pipe 159connects to a foreline valve 160 which connects through pipe 161 to apipe 162. Pipe 162 connects to a rough line valve 163 to a pipe 164which connects to pipes 138, 154.

Pipes 158, 159 connect through pipe 165 to a hold line valve 166. Saidvalve 166 is connected to pipe 167 which connects to solenoid valve 168.Said valve 168 is connected through pipe 169 to a holding pump 170.

Pipes 161, 162 are connected through pipe 171 to a mechanical pump 172.

The compacts or parts to be heat treated are placed on pans 181 whichare stacked in spaced relation in the pot 40 by means of spacers 182.The pans 181 have center holes 183 which are aligned with hole 44.

The pans 181 with the parts 180 thereon may be stacked in pot 40 to thetop.

At the beginning, the graphite chimney and thermocouple are in place asshown in FIG. 1. Hydrogen is flowed through pipe 27 to pipe 24, butsupply of argon to pipe 24 is shut off. Argon is supplied to port orpipe 50 at the same time.

The metal powders (tungsten carbide) are compacted as usual, cold, inorder to make a part out of them. As the press friction is very great,the metal contains a lubricant or binder such as paratfin.

Heretofore, a pre-sintering was performed in either a hydrogen furnaceor a vacuum furnace. The sintering process was also performed in ahydrogen 'furnace' or a vacuum furnace. However, the part first wententirely through the pre-sintering cycle including pre-heat, heat, andcool down, and when it cooled to room temperature, it was transferred toa sintering furnace for the sintering cycle. It was difficult to get ridof all the waxes which were trapped.

In accordance with the present invention the de-waxing in hydrogen andsintering in vacuum is accomplished in the single vessel withouttransfer.

There is also on the market a furnace which heat treats compacts in avessel with various chambers, done in a vacuum chamber, but the compacthas to be moved from one area to another to perform the variousfunctions.

In the present invention, an atmospheric de-waxing operation isperformed in hydrogen, and the same vessel is used for vacuum sinteringwithout moving the part to be heat treated and in one continuousoperation.

The cycle of the operation of the apparatus described is as follows: Thechamber 90 is filled with argon. The argon enters container 11 throughpipe or port 50 and passes through openings 104a into chamber 90. Theinner pot 40 is filled with hydrogen. As the temperature increases, theparts Will be de-waxed. The waxes will volatilize and pass up to theatmosphere through the graphite chimney 85. The argon protects thegraphite components from oxidizing by excluding the air. The argonpressure is heavier than air and protects the elements.

The hydrogen burning at the top of the graphite chimney thereby burnsthe volatilized waxes. No air can mix so that the hydrogen burns andputs the Wax vapors into the atmosphere. The de-waxing is carried out atabout 400 C. The hydrogen prevents oxidation of the compacts.

The liberated wax would break down if it contacted the heating elements.With the present apparatus this is avoided by keeping the waxes separateso that they cannot reach the heating elements.

When temperature has been reached where all waxes have been volatilized,the supply of hydrogen to the pot is shut off and argon is flowed intothe pot. The flushed out hydrogen burns at the top.

Argon is now inside of the pot and outside of the pot, and thetemperature is still at 400 C. When the hydrogen fiame goes out we knowthat argon is in the pot.

The graphite tube 85 and the thermo-couple 86a are now removed throughthe water cooled port 69, and a sight glass 190 will be placed over theport (FIG. 4), with an O-ring 191, placed between the sight glass andthe upper surface of flange 76. Then all argon fiow will be stoppedthrough pipes 50 and 28.

The vacuum system will then be started and argon will be pumped out orexhausted from the chamber and pot. A vacuum suitable for sintering thecompact will be achieved by means of the mechanical pump 172 and boosterpump 157, the holding pump 170 being merely used to protect the boosterpump.

The electric input to the heating elements is increased when theprescribed vacuum pressure has been achieved. At about 750 the compactsare presintered and at about 1450" C. the compacts are sintered. Thepresintering is accomplished as the temperature rises from the dewaxingtemperature to the sintering temperature. There is no cool-down betweenpresintering and sintering. It is not necessary because the parts arenot handled between dewaxing and sintering.

The flow of cooling water in jacket 75 and the provision of the rubberheat insulating tube on the tube 74 keep the port 69 cool. Thecondensible gases flowing up are attracted to the inside surface of tube73 and keeps the sight glass from clouding up.

Thus the cooled port has two functions.

(1) It keeps the graphite chimney cool and stops it *from' oxidizing(while the 'chimney is'in place); and" (2) Under vacuum operation, whenthe graphite chimney has been removed, and the sight glass has beeninstalled, the sight glass is prevented from clouding up by preventingcondensible vapors from settling on the sight glass and clouding itthereby preventing actual temperature reading.

The operator looking down through the sight glass and through opening183 in pans 181 can observe the color to judge the temperature.

After sintering is completed, and the heating units turned off, thecompacts may be cooled by supplying helium to the pipe 50 from thehelium supply 137.

It will thus be seen that there is provided an article in which theseveral objects of this invention are achieved, and which is welladapted to meet the conditions of practical use.

As possible embodiments might be made of the above invention, and asvarious changes might be made in the embodiments above set forth, it isto be understood that all matter herein set forth or shown in theaccompanying drawings, is to be interpreted as illustrative only.

I claim:

1. A process for treating powder metal compacts comprising placing thecompacts in a pot open to the atmosphere and surrounded by a chamber,flowing a hydrogen comprising gas through the pot to the atmosphere, andan inert gas to the chamber, heating the pot and burning the hydrogencomprising gas to the atmosphere to dewax the compacts, then flushingout the hydrogen comprising gas from the pot to the atmosphere with aninert gas flowed into the pot, then pumping out the inert gases from thepot and from the chamber by creating vacuum therein, and increasing theheat in the chamber to sinter the compacts.

2. The process of claim 1, wherein the pot is closed to the atmosphereand opened to the chamber after the hydrogen is flushed out of the potto the atmosphere.

3. A process for treating a powdered metal compact, said compactcontaining a volatilizable wax, which process comprises placing thecompact into a pot having a passage to the air, supplying a flow of anon-oxidizing gas to the pot and out the passage to exclude air from thepot, heating the pot to a temperature to volatilize said wax from saidcompact and said gas causing the volatilized wax to fiow out throughsaid passage and burn in the air, said gas continuing to exclude airfrom the pot to prevent oxidizing of the compact during dewaxing of thecompact, creating a vacuum in the pot, and heating the pot to atemperature to sinter the compact in vacuum, without having to removethe compact from the pot.

4. The process of claim 3, wherein the temperature is raised to about400 C. in the pot during de-waxing and is raised to about 1450 C. forthe sintering operation.

5. The process of claim 3, wherein the gas is flushed out of the pot byshutting off supply thereof to the pot and then supplying an inert gasto the pot before creating vacuum to remove the inert gas from said pot.

6. The process of claim 3, then shutting off the heat,

ceasing creation of vacuum and cooling the pot by introducing heliuminto said pot.

7. The combination of claim wherein said inert gas comprises argon.

8. The process of claim 3, wherein said non-oxidizing gas is a gascomprising hydrogen.

9. The process of claim 8, wherein said gas comprising hydrogen isdissociated ammonia.

10. The process of claim 8, which further comprises burning the hydrogenin the air together with burning of said volatilized Waxes.

11. A process for heat treating powdered metal compacts comprisingde-waxing the compacts in a vessel which opens to the atmosphere byflowing hydrogen comprising gas into the vessel and heating the vesselto burn the gas in the atmosphere, then flushing out the'hydrogencomprising gas from the vessel by shutting ofi flow of said hydrogencomprising gas to said vessel, and flowing an inert gas into saidvessel, then removing said inert compacts in vacuum without removing thecompacts from said vessel.

References Cited UNITED STATES PATENTS 2,363,575 11/1944 De Lamatter eta1. 75--204 X 2,205,386 6/1940 Balke et a1. 75-221 X 2,185,410 1/1940Lederer 75221 X FOREIGN PATENTS 1,005,179 9/ 1965 Great Britain 75221OTHER REFERENCES Schwarzkopf, P. et al., Cemented Carbides, MacMillan,1960, pp. 38-9.

CARL D. QUARFORTH, Primary Examiner R. E. SCHAFER, Assistant ExaminerUS. Cl. X.R.

